Patterns are not just the visual representations of colors and shapes (like stripes, polka dots, or a wall of bricks); patterns also explain how our entire world is built with molecules - the tiny building blocks of our world that go beyond what our naked eye can see. Molecules are the Lego blocks of life.
Crystals and gemstones have a very special trait about them: their molecules come together to create patterns. Each type of molecular pattern is what defines different types of crystals and makes them unique.
Here is a very simple, 3-D pattern of a crystal's molecules that you see every day in your house:
Look at each smaller cube of molecules within the larger cube. Do you see the same cube of molecules over and over again? This crystal - that is, common salt - is created by this special formation of molecules repeating over and over again in 3 dimensions!
Here's another, more complicated pattern of molecules that make up another crystal:
This one is garnet! The beautiful gemstone we use in fancy pieces of jewelry looks quite different at the molecular level. With such a complicated collection of molecules, it's challenging to see the patterns, but look carefully - they are there!
One last pattern of crystal molecules:
This one is sugar! A selection of the pattern has been outlined in its center. You can then look at the entire picture and see the same pattern growing in every direction. Additionally, while this picture is 2D, sugar crystal molecules grow - of course - in 3 dimensions.
So what does any of this have to do with growing rock candy?
We know that pouring sugar into water will cause the sugar to dissolve, but when we pour sugar into hot water, the higher temperature causes more breaking apart of the sugar's molecular pattern. In other words, even more sugar dissolves in the water. But as the water cools, the separated sugar molecules re-form bonds with each other, forming a single and more massive pattern of molecules - rock candy!
The key to growing successful rock candy is creating a super-saturated solution of sugar water.
What does super-saturated mean?
In terms of sugar and water, a solution is saturated when you keep pouring and dissolving sugar into water up until the water cannot dissolve any more sugar. This point of equilibrium is saturation.
However, the hotter water can break apart more molecular patterns of sugar, allowing more sugar to be dissolved at the higher temperature than if the water was room temperature. This is super saturation. Then, once the water cools, it can no longer retain the same level of dissolved sugar. This forces the molecular patterns of sugar to reform, being "pushed out" from its dissolved state in water, and re-form as new crystals.